If you doubt that life is a crapshoot, consider the fates of the spot-tailed and emerald shiners in Lake Michigan. They are both minnows, members of the genus Notropis, the largest genus of freshwater fish in North America. They both feed on aquatic insects and small crustacea. The largest spot-tailed shiners are six inches long. Emerald shiners are even smaller.
But then some changes occurred. First smelt and then alewives entered the lake. Both of these fish feed in the open water, eating tiny plankton–and the drifting eggs of minnows–well above the bottom. Suddenly the habits that had served the emerald shiner for thousands of years were no longer adaptive.
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I learned about the emerald shiner from Allen Feldman, my principal consultant on matters ichthyological. Allen used to run the Great Lakes exhibits at the Shedd Aquarium, and he recently spoke at a meeting of the Lake Michigan Federation on the changes that have occurred in our fish since Europeans began to settle here.
Fish began to migrate into the newly formed Great Lakes as soon as the glaciers that created them receded. Coregonids–whitefish, chubs, ciscos, lake herring–came from the Pacific Northwest. Bowfins, long-nosed gar, grass pickerel, arid suckers came from southern rivers–the Mississippi and its tributaries. Green sunfish, pumpkinseeds, and bluegills came from the south and east. About 180 species of fish lived in these lakes when Europeans began to settle on their shores.
The destruction of the native ecosystems of the Great Lakes began in the 1830s, when fishermen settled in villages on the upper lakes–Huron, Superior, and Michigan–and began harvesting whitefish and lake herring. They cleaned and salted the fish and packed them in barrels for shipment to the east. These species began to show serious declines within a few decades.
Lampreys entered the upper lakes through the Welland Canal, the waterway that allows vessels to get around Niagara Falls. In the ocean lampreys are no particular problem. They tend to go after very large fish, which can survive a temporary infestation. In the upper lakes they found no very large fish. Their feeding was a coup de grace for the lake trout, finishing the job the commercial fishermen started.
And the cost of maintaining a degraded and reduced commercial fishery and a sport fishery that provides only marginally edible fish is very high. Illinois spends about $750,000 a year to raise salmon and trout in its hatchery. But that cost is tiny. Michigan spends $4 million on its hatcheries for the same purpose. Controlling the sea lamprey costs as much as $15 million a year. Zebra-mussel control runs $4-5 million a year, and this will probably go up in the future. And there is no guarantee that the control program will be successful.
